1. Field of the Invention
The present invention relates to a compact, small-sized lighting device including at least two lamp units and having a high utilization efficiency of light. The present invention also pertains to a projector-type display apparatus with such a lighting device for producing bright projected images which are uniform in brightness.
2. Discussion of the Background
A lighting device incorporated in projector-type display apparatus generally has a lamp unit, which includes a light source lamp, such as a halogen lamp or a metal halide lamp, and a reflector for reflecting an incident ray emitted from the light source lamp and outputting the reflected ray as a parallel beam or a converging beam in a predetermined direction. Available reflectors have the reflecting surfaces in the shape of paraboloid or ellipsoid.
It is preferable that the lighting device used in the projector-type display apparatus has a large output quantity of light, in order to produce uniform and bright projected images. Further a compact, small-sized lighting device is desirable when being incorporated in portable projector-type display apparatus.
The lighting device may include a plurality of lamp units, for example, two lamp units, in order to increase the output quantity of light. A simple array of the two lamp units in parallel, however, doubles the width of the lighting device and makes the lighting device undesirably bulky. This arrangement also doubles the width of the flux of output light and requires an extended width of the optical path in the lighting device. This further doubles the required width of the optical path formed in the projector-type display apparatus with such a lighting device incorporated therein. This arrangement is thus not suitable for the requirement of the compact, small-sized structure.
A typical example of the lighting device incorporated in the projector-type display apparatus is a lamp unit including a light source lamp having a short arc length and a reflector of a paraboloidal shape having a short focal distance. The distribution of the quantity of light emitted from the lamp unit of this structure is shown as a characteristic curve that has a sharp peak on and in the vicinity of a lamp optical axis and abruptly decreases with a distance from the lamp optical axis. The use of only the light fluxes in a central portion including the lamp optical axis for illumination does not significantly lower the quantity of light.
The object of the present invention is thus to provide a technique for providing a lighting device with a plurality of lamp units and a projector-type display apparatus with such a lighting device incorporated therein, which can produce projection images that are bright, uniform in brightness, and even in color.
(First Lighting Device and Projector-type Display Apparatus therewith)
At least part of the above and the other related objects is attained by a first lighting device of the present invention, which includes a lamp unit having a light source lamp and a reflector for reflecting light emitted from the light source lamp, the lighting device further including a plurality of the lamp units arrayed in a direction perpendicular to an optical axis of the light source lamp, wherein the reflector of each the lamp unit has a shape obtained through cutting a concave surface of revolution, which is obtained by rotating a curve about the optical axis of the light source lamp, on at least one end adjoining to another lamp unit by a plane substantially perpendicular to a direction of the array of the lamp units.
The plurality of lamp units may be arrayed in one direction substantially perpendicular to the optical axis of the light source lamp, or in two directions each substantially perpendicular to the optical axis of the light source lamp.
In a lamp unit with a reflector, the quantity of output light is extremely large in a central portion including an optical axis of a light source lamp and decreases with a distance from the optical axis of the light source lamp. In the first lighting device of the present invention, the reflector of each lamp unit is cut to have a narrow width. This reduces the total width of the lighting device. This structure with narrow reflectors effectively utilizes the output light in the central portion including the lamp optical axis and thereby ensures a sufficient amount of output light. The lighting device of the present invention ensures a greater quantity of output light, while having substantially the same size as that of the conventional lighting device with only one lamp unit. The lighting device of the present invention is preferably used as a light source of a projector-type display apparatus that displays bright projection images.
In accordance with one preferable application, the reflector has a shape obtained through both ends of the concave surface of revolution by the plane substantially perpendicular to the direction of the array of the lamp units, and a distance between both of cut faces is approximately half a diameter of an opening of the concave surface of revolution. Especially two lamp units arrayed in one direction have the quantity of output light as much as about 1.5 times the conventional lighting device with a single lamp unit, while making the width of the lighting device substantially the same. This arrangement enables the projector-type display apparatus to utilize an optical system designed for a lamp unit having a reflector with no side cuts.
In accordance with another preferable application, the reflectors included in the plurality of lamp units are optically integrated with one another. This facilitates the manufacture of the lighting device. The term xe2x80x98optically integratedxe2x80x99 means that the respective optical elements are in close contact with one another. The plurality of optical elements may be optically integrated by bonding them with an adhesive or by integrally forming them.
One preferable structure enables one of the light source lamps included in the plurality of lamp units to be selectively turned on. This structure enables the brightness of light to be adjusted in multiple steps if required, thereby attaining the required brightness and efficient power consumption.
In accordance with another preferable structure, the light source lamps included in the plurality of lamp units emit respective light of different wavelength distribution characteristics. This structure enables the tint of light for illumination to be set to a predetermined value, thereby improving the color reproducibility of a color projector-type display apparatus.
The lighting device preferably has an integrator optical system, in order to reduce the unevenness of illuminance of light output from the lighting device. Namely the lighting device further includes an integrator optical system having a first lens plate including a plurality of lenses and a second lens plate including a plurality of lenses, wherein the first lens plate spatially divides the light emitted from the light source lamp by the plurality of lenses included therein to produce a plurality of intermediate light fluxes, which are focused as secondary light source images in the vicinity of entrance planes of the plurality of lenses included in the second lens plate, output via the plurality of lenses included in the second lens plate, and superposed on a predetermined illumination area. Even when there is a significant variation of the intensity of light within a cross section of the light flux emitted from the lamp unit, the above structure enables the output light to be uniform in brightness and even in color.
In one preferable application of this structure, the lighting device further includes polarizing means for converting light fluxes output from the second lens plate to light fluxes of a single polarization type having identical polarizing directions and outputting the light fluxes of the single polarization type. The polarizing means has polarization separating means for separating the light fluxes output from the second lens plate into light fluxes of two polarization types having different polarizing directions; and polarization converting means for converting the polarizing direction of one of the light fluxes of the two polarization types obtained by the polarization separating means to the polarizing direction of the other of the light fluxes of the two polarization types, wherein the predetermined illumination area is illuminated with the polarized light fluxes of the single type having identical polarizing directions obtained by the polarizing means.
Since this structure uses only the light fluxes of a single polarization type having substantially identical polarizing directions for illumination, the utilization efficiency of light is improved when the lighting device is incorporated in, for example, a projector-type display apparatus as discussed below. Light absorption hardly occurs in the process of converting the light fluxes of random polarizing directions to the polarized light fluxes of a single polarization type having substantially identical polarizing directions. This gives specific polarized light fluxes with an extremely high efficiency.
The lighting device discussed above may be used as a light source of a projector-type display apparatus. The projector-type display apparatus includes the first lighting device of the present invention described above, modulation means for modulating light emitted from the lighting device responsive to image information, and a projection optical system for projecting a modulated light flux obtained by the modulation means onto a projection plane. As described above, the first lighting device of the present invention ensures a greater quantity of output light, while having substantially the same size as that of the conventional lighting device. The projector-type display apparatus using the first lighting device as the light source produces projection images of the improved brightness, while having substantially the same size as that of the conventional apparatus with a single lamp unit.
In case that the lighting device has an integrator optical system, even when there is a significant variation of the intensity of light within a cross section of the light flux emitted from the lamp unit, this structure enables the modulation means to be illuminated evenly with the light of uniform brightness. The projector-type display apparatus accordingly produces a projection image that is uniform in brightness and even in color over the whole projection plane.
In accordance with one preferable application, the lighting device includes the polarizing means having the polarization separating means and the polarization converting means as described above. This structure enables the modulation means to be illuminated with light fluxes of a single polarization type having identical polarizing directions.
In the projector-type display apparatus with the modulation means utilizing light fluxes of a single polarization type, such as a liquid-crystal device, when the output light includes the light fluxes of random polarizing directions, polarization selecting means, such as a polarizing plate, is required to omit the polarized light fluxes of a different polarizing direction that is not used for the illumination. This extremely lowers the utilization efficiency of light. When the polarizing plate is used as the polarization selecting means, a powerful cooling device is required for cooling the polarizing plate, since absorption of light significantly increases the temperature of the polarizing plate. The above preferable structure, however, converts the light fluxes of random polarizing directions emitted from the light device to polarized light fluxes of a single polarization type having substantially identical polarizing directions and enables the modulation means to be illuminated with the light fluxes of a single polarization type having substantially identical polarizing directions. Namely this structure utilizes most of the light fluxes emitted from the light source lamps and produces extremely bright projection images. The light used for illumination and display includes little polarized light fluxes of a different polarizing direction, so that the amount of light absorbed by the polarizing plate is extremely small. This effectively prevents the temperature increase of the polarizing plate and remarkably reduces the size of the cooling device for cooling the polarizing plate.
In order to project and display color images, the projector-type display apparatus further includes color separation means for separating the light emitted from the lighting device into at least two color light fluxes; a plurality of the modulation means for modulating the respective color light fluxes separated by the color separation means; and color combining means for combining the color light fluxes modulated by the plurality of modulation means, wherein a composite light flux obtained by the color combining means is projected on the projection plane via the projection optical system.
(Second Lighting Device and Projector-type Display Apparatus therewith)
The present invention is also directed to a second lighting device for illuminating an illumination area of a substantially rectangular shape having sides parallel to either of a first direction and a second direction which are substantially perpendicular to each other. The second lighting device includes: a light source; a first lens plate having a plurality of small lenses for dividing a light flux emitted from the light source into a plurality of partial light fluxes and condensing the plurality of partial light fluxes; a second lens plate having a plurality of small lenses on which the plurality of partial light fluxes are incident; polarizing means comprising polarization separating means for separating each of the plurality of partial light fluxes output from the second lens plate into light fluxes of two polarization types having different polarizing directions, and polarization converting means for converting the polarizing direction of one of the light fluxes of the two polarization types obtained by the polarization separating means to the polarizing direction of the other of the light fluxes of the two polarization types, the polarizing means thereby converting the plurality of partial light fluxes to plural light fluxes of a single polarization type having substantially identical polarizing directions and outputting the plural light fluxes of the single polarization type; and superposing means for superposing the plural polarized light fluxes output from the polarizing means to illuminate the illumination area. The polarization separating means is arranged to cause the light fluxes of two polarization types to be spatially separated along the first direction of the illumination area. Each small lens of the first lens plate has a substantially rectangular shape when projected on a plane perpendicular to a central optical axis of the each small lens, wherein the substantially rectangular shape has an aspect ratio that is virtually equal to an aspect ratio of the illumination area, and the plurality of partial light fluxes output from the small lenses are incident on corresponding small lenses of the second lens plate. Each small lens of the second lens plate has a substantially rectangular shape when projected on a plane perpendicular to a central optical axis of the each small lens, wherein the substantially rectangular shape has an aspect ratio that is smaller than the aspect ratio of the illumination area. The aspect ratio is defined by a ratio of a length of the side parallel to the second direction to a length of the side parallel to the first direction.
Here the light flux passing through each small lens of the second lens plate is regarded as a set of illumination light flux. The attention is drawn to the aspect ratio of the cross section of the illumination light flux. In the second lighting device of the present invention, the second lens plate includes the small lenses having the aspect ratio that is smaller than the aspect ratio of the small lenses of the first lens plate (which is virtually identical with the aspect ratio of the illumination area). The aspect ratio of the set of illumination light flux is accordingly smaller than the aspect ratio of another set of illumination light flux which would be obtained when the second lens plate had a plurality of small lenses having the aspect ratio that is identical with the aspect ratio of the small lenses of the first lens plate. The cross section of the illumination light flux is accordingly rectangular, wherein the length of the first direction is greater than the length of the second direction, corresponding to the aspect ratio of the small lenses of the second lens plate. (Among the sets of illumination light fluxes passing through the second lens plate, the illumination light flux having the aspect ratio of its cross section corresponding to the aspect ratio of the small lenses of the second lens plate is hereinafter referred to as the xe2x80x98compressed illumination light fluxxe2x80x99, whereas the illumination light flux having the aspect ratio of its cross section corresponding to the aspect ratio of the small lenses of the first lens plate is hereinafter referred to as the xe2x80x98non-compressed illumination light fluxxe2x80x99.)
When the lighting device of this structure is applied to a projector-type display apparatus, a projection plane is illuminated with the compressed illumination light fluxes via a projection lens. Compared with the non-compressed illumination light flux, the compressed illumination light flux has a smaller incident angle, at which the light flux enters the projection lens, and enables a greater amount of illumination light fluxes to enter on and in the vicinity of the center of the lens pupil of the projection lens. The utilization efficiency of light in a lens is generally higher at the position nearer to the center of the lens pupil and worsens toward the periphery. Application of the second lighting device of the present invention to the projector-type display apparatus enables the light emitted from the light source to be utilized efficiently and displays uniform and bright projection images.
The plurality of small lenses of the second lens plate, which have the smaller aspect ratio than that of the small lenses of the first lens plate, are arranged to have substantially the same dimensions as those of a shape when projected on a plane perpendicular to the central optical axis of the second lens plate, which includes a plurality of small lenses having the same aspect ratio as that of the small lenses of the first lens plate. The number of the small lenses of the second lens plate is identical with the number of the small lenses of the first lens plate. The reflector of the lamp unit is increased in size corresponding to the dimensions of a shape when projected on a plane perpendicular to the central optical axis of the first lens plate. This increases the utilization efficiency of the light fluxes emitted from the light source lamp, without increasing the sectional dimensions of the optical system except the reflector, compared with the conventional lighting device with the second lens plate which includes small lenses having the same aspect ratio as that of the small lenses of the first lens plate.
In order to obtain the equivalent quantity of the compressed illumination light fluxes to that of the non-compressed illumination light fluxes, the optical elements in each optical system, which the light output from the second lens plate passes through, have smaller required dimensions along the second direction. This desirably reduces the size of the lighting device as well as the size of the projector-type display apparatus with such a lighting device incorporated therein.
In accordance with one preferable application, the light source includes a plurality of lamp units arrayed in the second direction, each the lamp unit having a light source lamp and a reflector for reflecting light emitted from the light source lamp. Although requiring the additional space for the plurality of lamp units, the lighting device of this structure increases the quantity of output light.
When this lighting device is applied to the projector-type display apparatus, the rays emitted from the plurality of lamp units are deviated in a substantially symmetrical manner along the second direction with respect to the central optical axis of the second lens plate, when passing through the projection lens. As described above, the utilization efficiency of light in a lens is generally higher at the position nearer to the center of the lens pupil and worsens toward the periphery. As described in the prior art, the quantity of light output from one lamp unit is extremely large in a central portion including an optical axis of a light source lamp and abruptly decreases with a distance apart from the optical axis of the light source lamp. In the lighting device of the above structure, the width of the light output from each lamp unit along the second direction is compressed about the central optical axis of the second lens plate. This enables the rays emitted from the plurality of lamp units to be led to the projection lens with a high efficiency and realizes bright projection images.
The second lighting device of the present invention has the integrator optical system including the first lens plate, the second lens plate, and the superposing means, thereby effectively reducing the unevenness of illuminance of light. The second lighting device also has the polarizing means that generates light fluxes of s single polarization type having substantially identical polarizing directions as the light of illumination. This structure utilizes most of the light fluxes emitted from the light source lamp and thereby improves the utilization efficiency of light.
The plurality of partial light fluxes output from the first lens plate are focused in the vicinity of the second lens plate and the polarization separating means to form secondary light source images. The polarization separating means divides each incident light flux along the first direction into two types of polarized light fluxes, so that two secondary light source images are formed in alignment along the first direction on the polarization separating means. It is accordingly desirable that the dimensions of the polarization separating means are substantially identical with or greater than the dimensions of the two secondary light source images aligned along the first direction. When the dimension along the first direction of each small lens included in the second lens plate is substantially the same as the dimension along the first direction of the polarization separating means, the respective smalls lenses of the second lens plate and the polarization separating means can be arranged at the highest efficiency without any clearances. The value of the aspect ratio of each small lens of the second lens plate may be set equal to approximately xc2xd by taking into account the efficiency of arrangement of the respective small lenses of the second lens plate and the polarization separating means, when the secondary light source images are approximated to have a substantially circular shape. This arrangement reduces the size of the second lens plate without causing a light loss. This structure enables the light emitted from the light source to be efficiently utilized and obtains a large quantity of light for illumination.
In the lamp unit generally applied, the rays emitted from the light source lamp are reflected by the reflector and output as parallel rays. The parallelism of the output light from the lamp unit is worse at the position closer to the lamp optical axis and improved with a distance from the lamp optical axis. The secondary light source images formed by the plurality of partial light fluxes in the vicinity of the second lens plate and the polarization separating means are smaller at the position farther from the center of the second lens plate. It is accordingly preferable that the plurality of small lenses of the second lens plate arranged in a plurality of rows along the second direction are adjusted to have the dimension along the second direction that decreases with their distances from the center position of the light flux emitted from the light source.
This structure more efficiently decreases the width along the second direction of the set of illumination light flux passing through the second lens plate. This accordingly reduces the sizes of the second lens plate and the polarizing means and improves the utilization efficiency of light output from the light source.
In the lighting device with the array of the plurality of lamp units, the reflector of each the lamp unit may have a shape obtained through cutting a concave surface of revolution, which is obtained by rotating a curve about the optical axis of the light source lamp, on at least one end adjoining to another lamp unit by a plane substantially perpendicular to a direction of the array of the lamp units.
In a lamp unit with a reflector, the quantity of output light is extremely large in a central portion including an optical axis of a light source lamp and decreases with a distance from the optical axis of the light source lamp. In the lighting device of the above structure, the reflector of each lamp unit is cut to have a narrow width. This reduces the total width of the lighting device. This structure with narrow reflectors effectively utilizes the output light in the central portion including the lamp optical axis and thereby ensures a sufficient amount of output light. The lighting device of the present invention ensures a greater quantity of output light, while having substantially the same size as that of the conventional lighting device with only one lamp unit. The lighting device of the present invention is preferably used as a light source of a projector-type display apparatus that displays bright projection images.
The lighting device discussed above may be used as a light source of a projector-type display apparatus. The projector-type display apparatus includes the second lighting device of the present invention discussed above, modulation means for modulating light emitted from the lighting device responsive to image information, and a projection optical system for projecting a modulated light flux obtained by the modulation means onto a projection plane. As described above, the second lighting device of the present invention efficiently utilizes the light emitted from the light source and obtains a large quantity of light for illumination. The projector-type display apparatus using the second lighting device as the light source produces projection images of the improved brightness, while having substantially the same size as that of the conventional apparatus with a single lamp unit.
The second lighting device of the present invention has the integrator optical system as discussed above. Even when there is a significant variation of the intensity of light within a cross section of the light flux emitted from the lamp unit, this structure enables the modulation means to be illuminated evenly with the light of uniform brightness. The projector-type display apparatus accordingly produces a projection image that is uniform in brightness and even in color over the whole projection plane.
The second lighting device of the present invention has the polarizing means including the polarization separating means and the polarization converting means and enables the modulation means to be illuminated with light fluxes of a single polarization type having substantially identical polarizing directions. In the projector-type display apparatus with the modulation means utilizing light fluxes of a single polarization type, such as a liquid-crystal device, this structure utilizes most of the light fluxes emitted from the light source lamps and produces extremely bright projection images. The light used for illumination and display includes little polarized light fluxes of a different polarizing direction, so that the amount of light absorbed by the polarizing plate is extremely small. This effectively prevents the temperature increase of the polarizing plate and remarkably reduces the size of the cooling device for cooling the polarizing plate.
In order to project and display color images, the projector-type display apparatus further includes color separation means for separating the light emitted from the lighting device into at least two color light fluxes; a plurality of the modulation means for modulating the respective color light fluxes separated by the color separation means; and color combining means for combining the color light fluxes modulated by the plurality of modulation means, wherein a composite light flux obtained by the color combining means is projected on the projection plane via the projection optical system.
(Third and Fourth Projector-type Display Apparatuses)
The present invention is also directed to a third projector-type display apparatus including: a lighting device having a plurality of lamp units, each the lamp unit including a light source lamp and a reflector for reflecting light emitted from the light source lamp; color separation means for separating light emitted from the lighting device into at least two color light fluxes; and a plurality of modulation means for modulating the respective color light fluxes separated by the color separation means. The third projector-type display apparatus further includes: color combining means for combining the color light fluxes modulated by the plurality of modulation means; and a projection optical system for projecting a composite light flux obtained by the color combining means onto a projection plane. When x, y, and z denote three directional axes perpendicular to one another and z represents a direction parallel to an optical axis of light emitted from the lamp unit, the color separation means has a color separation plane that is substantially perpendicular to an x-z plane and has predetermined angles with respect to a y-z plane and an x-y plane, and the plurality of lamp units are arrayed substantially along the y direction.
The third projector-type display apparatus of the present invention thus constructed requires the additional space for the plurality of lamp units, but effectively enhances the quantity of light emitted from the lighting device. Each lamp unit is arranged in a direction perpendicular to the light-dividing direction of a dichroic surface of the color separation means, so that the rays emitted from the respective lamp units enter the dichroic surface at an identical incident angle. This structure effectively reduces color shift of each color light flux output from the dichroic surface to the modulation means. This accordingly enables an illumination area to be illuminated evenly with the light of uniform brightness.
The present invention is further directed to a fourth projector-type display apparatus including: a lighting device having a plurality of lamp units, each the lamp unit including a light source lamp and a reflector for reflecting light emitted from the light source lamp; color separation means for separating light emitted from the lighting device into at least two color light fluxes; and a plurality of modulation means for modulating the respective color light fluxes separated by the color separation means. The fourth projector-type display apparatus further includes: color combining means for combining the color light fluxes modulated by the plurality of modulation means; and a projection optical system for projecting a composite light flux obtained by the color combining means onto a projection plane. When x, y, and z denote three directional axes perpendicular to one another and z represents a direction parallel to an optical axis of light emitted from the lamp unit, the color combining means has a dichroic surface that is arranged to be substantially perpendicular to an x-z plane and have predetermined angles with respect to a y-z plane and an x-y plane, and the plurality of lamp units are arrayed substantially along the y direction.
Like the third projector-type display apparatus, the fourth projector-type display apparatus of the present invention thus constructed requires the additional space for the plurality of lamp units, but effectively enhances the quantity of light emitted from the lighting device. Each lamp unit is arranged in a direction perpendicular to the light-dividing direction of the dichroic surface of the color combining means, so that the rays emitted from the respective lamp units enter the dichroic surface at an identical incident angle. This structure effectively reduces color shift of the composite light flux output from the dichroic surface to the projection optical system. This accordingly produces a projection image of uniform brightness and even color.
In the third and the fourth projector-type display apparatuses of the present invention, the reflector of each the lamp unit may have a shape obtained through cutting a concave surface of revolution, which is obtained by rotating a curve about the optical axis of the light source lamp, on at least one end adjoining to another lamp unit by a plane substantially perpendicular to a direction of the array of the lamp units. The reflectors of this arrangement decrease the area occupied by the lamp units and thereby reduce the size of the projector-type display apparatus. These reflectors enable the rays in central portions including lamp optical axes to be effectively utilized and ensure the sufficient quantity of output light. This accordingly enables uniform and bright projection images to be projected and displayed.
In order to eliminate the unevenness of illuminance of light in the third and the fourth projector-type display apparatuses of the present invention, it is desirable that the lighting device has an integrator optical system. In a preferable structure, the lighting device has an integrator optical system including a first lens plate with a plurality of lenses and a second lens plate with a plurality of lenses. Even when there is a significant variation of the intensity of light within a cross section of the light flux emitted from the lamp unit, this structure gives the light of uniform brightness and even color. The projector-type display apparatus accordingly produces a projection image that is uniform in brightness and even in color over the whole projection plane.
In accordance with one preferable application, the lighting device has polarizing means for converting light fluxes output from the second lens plate to light fluxes of a single polarization type having identical polarizing directions. The illumination area is then illuminated with light fluxes of the single polarization type having identical polarizing directions, which are obtained by the polarizing means. This structure utilizes most of the light fluxes emitted from the light source lamps and produces extremely bright projection images. The light used for illumination and display includes little polarized light fluxes of a different polarizing direction, so that the amount of light absorbed by the polarizing plate is extremely small. This effectively prevents the temperature increase of the polarizing plate and remarkably reduces the size of the cooling device for cooling the polarizing plate.